The present invention relates generally to gas turbine buckets or blades and particularly relates to cooling a so-called platform portion interposed between the bucket airfoil and the bucket shank.
Over the years, gas turbines have trended toward increased inlet firing temperatures to improve output and engine efficiencies. As hot gas path temperatures have increased, however, bucket platforms have increasingly exhibited distress including oxidation, creep and low-cycle fatigue cracking, spallation and in some cases, platform liberation. With the advent of closed circuit steam cooling in, for example, the buckets and nozzles in the first two stages of industrial gas turbines, inlet profiles have become such that the bucket platforms are exposed to temperatures close to peak inlet temperatures for the blade row. The problem is particularly acute at the leading edge fillet where the airfoil joins the platform at the forward portion of the pressure side of the airfoil.
Accordingly, it would be beneficial if more effective cooling arrangements can be designed to cool the platform areas of buckets used particularly in the first and second stages of the turbine.